Apparatus and methods for leak detection in bioprocessing bags

ABSTRACT

An apparatus detects a leak of an electrically conductive fluid from a disposable plastic bag used in mixing applications, such as during bioprocessing in a sterile environment. In one embodiment, the bag is associated with a sensor for detecting a leak from an interior compartment. The sensor may be arranged to detect either a leak internal to the at least two material layers of the bag or external to the outer layer, or both. Related methods are also disclosed.

This application is a continuation-in-part of Ser. No. 11/689,761, nowU.S. Pat. No. ______, which is a continuation of InternationalApplication PCT/U.S.07/64492, filed Mar. 21, 2007, which claims thebenefit of U.S. Provisional Patent App. Ser. No. 60/784,615, filed Mar.22, 2006, the disclosures of which are all incorporated herein byreference.

TECHNICAL FIELD

The present invention relates generally to fluid processing and, moreparticularly, to apparatus and methods for detecting leaks that mayresult during the processing of fluids under sterile conditions.

BACKGROUND OF THE INVENTION

Many manufacturers of products requiring a temporary holding, mixing orother fluid processing step as part of the manufacturing process now optto use disposable bags for holding and contacting the fluid understerile conditions instead of rigid mixing tanks or vessels.Advantageously, such bags are relatively inexpensive to manufacture,easy to transport, store, and sterilize, and can be disposed of once theoperation is complete and any product recovered. Moreover, the use ofsuch bags not only both eliminates the need for cleaning and the chancefor cross-contamination, but also reduces the overall process cost.

A frequent problem encountered by users of such bags, which aretypically made of one or more layers of thin, fluid-impervious plasticfilm, is the risk of undesirable leakage. In the case of bioprocessingapplications, such leaks result in the loss of sterility inside the bagor the release of potentially hazardous biological material. If notdetected, such leakage can thus compromise the entire mixing operationand render the end product unsuitable for use. However, early detectionof such leakage can advantageously lead to appropriate corrective actionbeing taken, such as before the end product is distributed.

Up to now, leakage in these types of processing bags has been difficultto detect in a reliable fashion. Usually, such leakage is discoveredvisually in the form of wetness on the outside surface of the bag,spills on the floor and so on. Of course, this method of detection isnot reliable, since such wetness may result from the condensation on thebag outer surface, and unidentified spills can arise from other sources.Also, many leaks cannot be detected visually if the bag is kept in theclosed non-transparent container.

In the particular case of bioprocessing, most of the biological fluidsheld, stored or processed in bags comprise liquids, such as water basedelectrolytes, that are relatively good electrical conductors. Thematerial comprising the bag, on the other hand, is typicallypolyethylene or other plastic which is very good electrical insulator.The bags containing biological fluids can have just one layer of plasticfilm or several layers of film. In the latter case, the fluid touchinglayer of the bag usually has the best leachable and extractablecharacteristics to minimize the contamination of the processed fluidwith molecules diffused out of the plastic to the fluid. This layer istypically low density polyethylene. However, this innermost layer haspoor mechanical strength, and thus one or more additional layers areadded to enhance the mechanical strength of the bag.

The external layer(s) are not supposed to touch the processed fluid butprovide for the mechanical strength of the bag. Even though those layersare also sterile on the inner side, they may leach substantial amount oforganic molecules if they contact fluid as a result of the internalleak. Consequently, the leaks that can develop in the bags can be of twotypes:

-   -   1. Internal leaks where the electrically conductive fluid in the        interior compartment of the bag through only one or several        layers of the film but does not leak outside of the bag; or    -   2. External leaks, where the conductive fluid leaks to the        outside non-sterile environment.        Both types of leaks can potentially contaminate the product in        the bag and thus are highly undesirable.

Accordingly, a need exists for an expedient, yet reliable manner fordetecting either or both of these types of leaks, thereby allowing forimmediate corrective action to be taken.

SUMMARY OF THE INVENTION

An apparatus is provided for use with a sensor for sensing the presenceof a leak of a fluid held under sterile conditions. The apparatuscomprises a vessel including a flexible portion, said vessel at leastpartially defining an interior compartment adapted for receiving thefluid under sterile conditions. At least one electrode integrallyconnected to the vessel is adapted for use with the sensor for sensing aleak of the fluid. Sensing of the leak by the sensor using the electrodeindicates a breach of the sterile conditions.

In one embodiment, the at least one electrode comprises a firstelectrode connected to the flexible portion of the vessel, and a secondelectrode is adapted to form an electrical connection with the firstelectrode in the presence of a leak. The second electrode may beconnected to the vessel, and may be external to the interior compartmentof the vessel. The vessel may also include a port for at least partiallyreceiving the at least one electrode, as well as a connector forconnecting the electrode with the fluid under sterile conditions.

A support structure may be provided for supporting the vessel. In oneembodiment, the support structure comprises a second electrode adaptedfor use with the sensor for sensing a leak of the fluid. Afluid-agitating element may also be positioned in the interiorcompartment of the vessel.

The first or second electrodes may be arranged at least partially in awall of the flexible vessel. The first electrode is arranged at leastpartially in contact with the fluid, and preferably extends at leastpartially within the interior compartment. Preferably, the secondelectrode is external to the interior compartment.

An apparatus for at least temporarily holding a fluid for processingunder sterile conditions is also provided. The apparatus comprises avessel having a flexible portion at least partially defining an interiorcompartment for receiving the fluid under sterile conditions. Theapparatus further comprises means for sensing a leak of the fluid. Thesensing means is at least partially connected to the vessel as anintegral part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a mixing arrangement including a bag ina rigid support container for possible use with fluids under sterileconditions;

FIG. 2 is a schematic diagram of a leak detection apparatus forming oneaspect of the present invention;

FIG. 3 is a schematic diagram illustrating an alternative embodiment ofthe leak detecting apparatus of FIG. 2;

FIG. 4 is a schematic diagram of a leak detection apparatus forminganother aspect of the present disclosure; and

FIG. 5 is a schematic diagram of a leak detection apparatus forming yetanother aspect of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the present invention relates primarily to apparatus andmethods for use in leak detection. A particularly advantageous use ofthe inventive apparatus and methods is in connection with bioprocessingapplications where fluid conductors, electrically conductive biologicalfluids (typically liquids comprising or consisting essentially ofwater), are at least temporarily held in thin-walled, flexible orcollapsible vessels, such as for example disposable bags made of one ormore layers of plastic film. As noted above, this type of vessel canadvantageously be disposed of once the operation is complete and anyproduct recovered. This type of arrangement thus not only botheliminates the need for cleaning and the chance for cross-contamination,but also reduces the overall process cost.

A particularly preferred use of such a processing bag is in a fluidmixing system. As shown in FIG. 1, the bag B is positioned in theinterior compartment of a rigid container C that serves as a supportstructure. The bag B further includes an interior compartment adaptedfor receiving and at least temporarily holding an electricallyconductive fluid F and, most preferably, a biologically active liquid.The volume of the bag B is generally greater than one liter, andpreferably on the order of 10 to 1,000 liters.

Means for agitating the fluid in the bag B, such as a magnetic impellerI rotated by an external motive device D may also be provided, as shown.Alternatively or in addition, the fluid agitating means may comprise asparger (not shown) for introducing a gas into the bag B. Additionaldetails of such fluid-agitating means may be found in commonly assigned,co-pending U.S. patent application Ser. No. 11/304,417, the disclosureof which is incorporated herein by reference.

One exemplary apparatus 10 for detecting leaks in such a bag B, which isespecially important when the sterility of the interior compartment mustbe maintained, is now described with reference to FIG. 2. Asillustrated, the apparatus 10 includes a leak sensor or means forsensing a leak comprising at least one (and preferably only one)electrically conductive electrode 12 associated with the bag B (which,although not shown, may include the agitating means, such as theimpeller I of FIG. 1). In this first embodiment, this electrode 12penetrates the corresponding wall of the bag B such that one end atleast partially contacts the liquid inside and the other end ispositioned external to the interior compartment. However, as will bedescribed below, it is not necessary for the electrode 12 to penetratethe sidewall of the bag B in order to make contact with the fluid F,even if the sterile conditions are to be maintained.

In this embodiment, the sensor further comprises a second electrode(alternately referred to as a conductor for purposes of clarity) alsoforming part of the sensor or means for sensing, but external to theinterior compartment of the bag B. Preferably, this second electrode orconductor comprises a conductive material forming at least part of asupportive structure for the bag B, such as a rigid container 14. Thiscontainer 14 is preferably formed entirely of a rigid, conductivematerial, such as stainless steel. The container 14 is arranged suchthat it least partially and preferably fully receives the bag B, bothwhen it is empty (that is, before the fluid is introduced) and also whenfilled. Although shown spaced apart in FIG. 2 for purposes of cleardifferentiation, it should be appreciated that, when the bag B is filledwith liquid, the interior surface of the container 14 is normally inintimate contact with external or outer surface of the bag (see, e.g.,bag B and container C in FIG. 1).

The sensor or sensing means of the apparatus 10 as illustrated forpurposes of this preferred embodiment further comprises: (1) a generator16 capable of generating DC (Direct current) or AC (Alternating current)voltage (e.g., a battery or alternator); and (2) a detector 18 capableof detecting DC or AC electric current. Suitable connections, such as bywires, interconnect the electrode 12, container 14, generator 16, anddetector 18 so as to form a circuit, the purpose of which is outlinedfurther in the following description.

In a simple embodiment, and as shown in FIG. 2, the first electrode 12comprises an elongated piece of metal material (and preferably one thatis corrosion-resistant, such as stainless steel). This electrode 12 maypenetrate through the wall via a port of the bag B. An annular hermeticseal S between the rod serving as the electrode 12 and the port of thebag B may be provided to maintain the sterile interior environmenttypically desired. However, the electrode could take any other form thatallows for the desired electrical contact with the conductor (e.g.,container 14) to be established.

In one preferred mode of use and in accordance with the practice of amethod of leak detection, the bag B is equipped with the electrode 12.As noted above, this may be accomplished by positioning the electrode 12so that it penetrates through the selected sidewall of the bag B (suchas the top wall) in a hermetic manner, as shown in FIG. 2. In any case,the result is that one end of the electrode 12 communicates with theinterior, potentially sterile environment of the bag B and is at leastpartially in contact with the conductive fluid F or liquid. In contrast,the other end of the electrode 12 projects outside of the bag B or isotherwise in communication with the external environment. As a result ofthe connection noted above, the electrode 12 forming part of the sensorfor purposes of this preferred first embodiment of the apparatus 10allows electrical contact to be established between the generator 16 andthe liquid held in the bag B.

As illustrated, the bag B associates intimately with the at least partlyconductive container 14 and is filled with the selected liquid or otherconductive fluid in need of mixing during the course of bioprocessing.One pole of the generator 16 is electrically connected to the electrode12 at the outer (non-sterile) end. The other pole of the generator 16 iselectrically connected to the conducting container 14 including the bagB. The electric current is measured in the circuit (which of course isnormally open in the illustrated embodiment) using the detector 18.

If there is no leak through the wall of the bag B, there is noelectrical continuity and thus no flow of electric current. In otherwords, the circuit including the electrode 12, container 14, generator16, and detector 18 remains open. Electric current is not detected orregistered, thus indicating a “no leak” state.

However, if a perforation or hole in the bag wall exists, the leakingliquid (note arrow L in FIG. 2) forms an electrical contact between theliquid in the bag B and container 14. This results in closed circuitthrough which electric current can flow from the generator 16 to thedetector 18, which indicates the presence of the leak. Although notnecessary for most applications, it may also be advantageous to pre-wetthe exterior surface of the bag B, as this will help to ensure that thecircuit is closed by even the smallest of leaks.

In the preferred embodiment, this detector 18 comprises a currentmeasuring device, such as an amp meter (in which case one of the pole ofthe generator 16 connects to the electrode 12 or to the container 14, asshown in FIG. 2). However, any suitable indicator to alert a user to theleak, such by creating a visual or aural signal, may be used. Theimportant point is that the presence of the leak is properly andpromptly identified such that suitable ameliorative measures may betaken.

As should be appreciated, the generator 16 and detector 18 may beincorporated in one device (not shown). This device can simply measurethe resistance of the circuit (which can of course be open or closed).In case of no leak (an open circuit), the resistance is very high.However, in case of a leak closing the circuit, the resistance wouldsharply drop and thereby indicate the presence of the leak.

As should be further appreciated, the electrode 12 can be pre-introducedduring manufacturing, in which case it would become an integral part ofthe bag B. Accordingly, the electrode 12 should be capable to withstandthe sterilization cycle performed on the bag B, such as Gamma radiationsterilization. Another option is to sterilize the electrode 12separately and introduce it via a tube T associated with a sterileconnection device K (such as a KLEENPAK device of Pall Corporation or aBIOQUATE aseptic disposable connector, manufactured by BioQuate Inc.).In such case, as shown in FIG. 3, the electrode 12 may not project intothe interior compartment of the bag B, despite making contact with thefluid F by way of the tube T.

As contrasted with external leaks, internal leaks develop when only oneor several layers of material (e.g., plastic film) have holes orperforations, but the external layer remains intact. In this situation,the fluid may be not coming out of the bag to the external environment,but rather may accumulate between the layers. To detect this kind ofleak, a leak detection apparatus 100 in accordance with another aspectof the invention is described.

In the preferred second embodiment of the apparatus 100 for detectinginternal leaks now being described, and with reference to FIG. 4, asensor is associated with and preferably arranged between at least twointernal and external layers of material forming layers L₁, L₂ of thebag B (which layers are normally in intimate contact, but are shownspaced apart for purposes of illustration). In one particularlypreferred embodiment, as shown in FIG. 3 (in which the proportions maybe considered altered for purposes of illustration), this sensorcomprises at least two electrodes 102 a, 102 b that are spaced apart orotherwise not in electrical contact in the absence of a leak. This maybe accomplished by separating the electrodes 102 a, 102 b by aninsulator 102 c (which if the second electrode 102 b comprises aconductive support structure, like container 14, could be considered thebag B). Preferably, as shown, the electrodes 102 a, 102 b are bothbetween the layers L₁, L₂, but penetrate the external layer L₂ only. Inother words, no part of the sensor is in contact with the interior ofthe bag B, which thus helps to ensure and maintain the desired sterileenvironment. Most preferably, the sensor is located along or adjacent abottom portion of the bag B for reasons that will be better understoodupon reviewing the following description.

As before, the apparatus 100 with the sensor further includes agenerator 116 capable of generating DC (Direct current) or AC(Alternating current) voltage; and (2) a detector 118 capable ofdetecting DC or AC electric current. Suitable connections, such as bywires, interconnect the electrodes 102 a, 102 b, generator 116, anddetector 118 so as to form a circuit (and preferably one that remainsopen in the absence of a leak from the internal layer L₁ in view of theinitially isolated electrodes 102 a, 102 b).

In using this embodiment and a corresponding method, the sensor isinitially such that no internal leak is detected. If the liquid leaksthrough the first (liquid touching) layer L₁ of the bag B, it may flowdown toward the bottom portion of the bag B and make contact theelectrodes 102 a, 102 b. Such contact closes the electric circuit suchthat current flow is established. Consequently, the detector 118indicates the presence of the leak, such as by indicating the flow ofelectric current.

FIG. 5 illustrates an embodiment in which the apparatus 10 includes abag B associated with a first electrode 12 and a second electrode 14comprising a stable support structure, (which is shown in the form of atable or cart for assisting in supporting the bag B), but could takeother forms. As with one or more of the previously describedembodiments, the electrodes 12, 14 are associated with a detector 18 anda generator (not shown). The bag B comprises an inner layer L₁ of agenerally non-conductive material, such as a polymer film, defining aninterior compartment for receiving a fluid F, and preferably arrangedsuch that contact with the first electrode 12 is made. A second,preferably outermost layer L₂ of the bag B comprises a conductivematerial, such as a metalized film, conducting mesh or like reticulatedstructure external to the interior compartment that may intimatelycontact the second electrode 14 in use, but remains electricallyisolated from the first electrode 12. A leak from the interiorcompartment of the bag B through the inner layer may thus connect thefluid F already contacting the first electrode 12 with the secondelectrode 14 (again, which comprises an outer layer of the bag B). Thiscompletes the circuit and forms an electrical connection, such that aleak can be detected using the detector 18, as described herein.

Summarizing the foregoing, apparatus 10 or 100 can be used to advantagein connection with bioprocessing applications where fluid conductors,such as electrically conductive biological fluids (typically liquids),are at least temporarily held in thin-walled, flexible or collapsiblevessels, such as for example disposable bags made of one or more layersof plastic film. A sensor includes electrodes 12, 14 or 102 a, 102 bthat may be connected by a leak, either internal to a multi-layeredvessel or external thereto, to a generator 16, 116. An associateddetector 18, 118 can detect the presence of the leak to allow forappropriate corrective action, thereby saving time and money.

The foregoing descriptions of various embodiments of the inventions arepresented for purposes of illustration and description, and are notintended to be exhaustive or limiting. Modifications are possible inview of the teachings provided herein. For instance, the invention couldbe used in an arrangement where the sensor associated with the flexiblevessel forms part of a normally closed circuit whereby the leak createsa short and thus opens the circuit. Additionally, both apparatus 10 andapparatus 100 may be used together for detecting internal and externalleaks. More than one sensor may also be provided in either apparatus 10,100. Although specifically proposed for use with a flexible bag, theapparatus 10, 100 may be used in connection with any vessel having aninterior compartment susceptible to leaking. The embodiments describedprovide the best illustration of the principles of the invention and itspractical applications to thereby enable one of ordinary skill in theart to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated.

1. An apparatus for use with a sensor for sensing the presence of a leakof a fluid held under sterile conditions, comprising: a vessel includinga flexible portion, said vessel at least partially defining an interiorcompartment adapted for receiving the fluid under sterile conditions;and at least one electrode integrally connected to the vessel, saidelectrode adapted for use with the sensor for sensing a leak of thefluid, whereby sensing of the leak by the sensor using the electrodeindicates a breach of the sterile conditions.
 2. The apparatus of claim1, wherein the at least one electrode comprises a first electrodeconnected to the flexible portion of the vessel.
 3. The apparatus ofclaim 2, further including a second electrode adapted to form anelectrical connection with the first electrode in the presence of aleak.
 4. The apparatus of claim 3, wherein the second electrode isconnected to the vessel.
 5. The apparatus of claim 3, wherein the secondelectrode is external to the interior compartment of the vessel.
 6. Theapparatus of claim 1, wherein the vessel includes a port for at leastpartially receiving the at least one electrode.
 7. The apparatus ofclaim 1, wherein the vessel includes a connector for connecting theelectrode with the fluid under sterile conditions.
 8. The apparatus ofclaim 1, further including a support structure for supporting thevessel.
 9. The apparatus of claim 1, wherein the support structurecomprises a second electrode adapted for use with the sensor for sensinga leak of the fluid.
 10. The apparatus of claim 1, further including afluid-agitating element positioned in the interior compartment of thevessel.
 11. The apparatus of claim 1, wherein the first electrodecomprises a layer of the vessel.
 12. An apparatus for at leasttemporarily holding a fluid for processing under sterile conditions,comprising: an at least partially flexible vessel having a firstinterior compartment capable of receiving the fluid for processing understerile conditions; and a sensor comprising a first electrode connectedto the vessel and a second electrode arranged external to the interiorcompartment to form an electrical connection with the first electrode,whereby the electrical connection between the first and secondelectrodes may be used to detect the presence of a leak of the fluidfrom the interior compartment of the flexible vessel.
 13. The apparatusof claim 12, wherein the first electrode is arranged to at leastpartially form a wall of the flexible vessel.
 14. The apparatus of claim12, wherein the second electrode is arranged to at least partially forma wall of the flexible vessel.
 15. The apparatus of claim 12, whereinthe first electrode is arranged at least partially in contact with thefluid.
 16. The apparatus of claim 12, wherein the first electrodeextends at least partially within the interior compartment.
 17. Theapparatus of claim 12, wherein the second electrode is external to theinterior compartment.
 18. The apparatus of claim 1, wherein the firstelectrode comprises a layer of the vessel.
 19. An apparatus for at leasttemporarily holding a fluid for processing under sterile conditions,comprising: a vessel having a flexible portion at least partiallydefining an interior compartment for receiving the fluid under sterileconditions; and means for sensing a leak of the fluid, said sensingmeans at least partially connected to the vessel as an integral partthereof.
 20. The apparatus of claim 19 wherein the sensing meanscomprises first and second electrodes arranged for forming an electricalconnection in the presence of a leak.
 21. The apparatus of claim 20further including a support structure for supporting the vessel.
 22. Theapparatus of claim 21, wherein the support structure comprises one ofthe first or second electrodes.